<html>
<head>
<style>
    .block {
        height:20px;
        width:100;
        margin:1px;
        background-color: #55A;
        -webkit-transition: all 100ms;
    }
    div.block:hover {
        height:50px;
    }
</style>
</head>
<body>
<div class="block">aaaa</div>
<div class="block">aaaa</div>
<div class="block">aaaa</div>
<div class="block">aaaa</div>
<div class="block">aaaa</div>
</body>
</html>
